Boiling water reactors (BWR) including a primary loop recirculation (PLR) system with a PLR pump to provide a flow of coolant for cooling to control an output of the reactor are known. In a BWR plant, a so-called MfG set including a variable speed hydraulic coupling for variably controlling a rotation speed of a motor coupled to the PLR pump is used as a PLR power supply to control a recirculation flow rate.
In the MfG set, power is supplied from a unit auxiliary middle voltage bus to an induction motor mechanically coupled to a variable rotation speed hydraulic coupling which is further mechanically coupled to a synchronous generator for generating power for driving the PLR pump motor, wherein the rotation speed control of the PLR pump motor is provided by controlling the variable speed hydraulic coupling. Upon controlling the flow rate in the core, kinetic momentum in the variable speed hydraulic coupling is controlled by a recirculation flow control signal from a reactor PLR control circuit to control the rotation speed of the PLR pump motor.
Another prior art PLR power supply for driving the PLR pump motor using a current source inverter instead of the MfG set in the nuclear power plant is disclosed in Japanese laid-open patent application No. 8-80061. In this prior art, the use of the current source inverter eliminates the necessity of the auxiliary devices of the MfG set such as the variable hydraulic coupling, a rotation machine, and a hydraulic device. This structure improves maintainability, efficiency in a low output condition, and linearity in speed control.